Zone 2 Training in Boise:
Is Your Water Holding You Back?

You're tracking your heart rate, logging your sessions, maybe even wearing a Garmin or Whoop. But if you're doing Zone 2 training in the Treasure Valley and drinking Boise tap water, there's a variable you probably haven't tested yet.

What Is Zone 2 Training and Why Is Everyone Doing It?

Zone 2 is the low-intensity cardio range that sits at 60-70% of your maximum heart rate. You can hold a conversation at this pace, and sessions typically run 45-60 minutes or longer. The adaptations it produces, improved mitochondrial density, better fat oxidation, stronger cardiovascular efficiency, are the foundation of what Peter Attia calls the "centenarian decathlon" in Outlive.

Andrew Huberman has dedicated multiple podcast episodes to it. Dr. Inigo San Millan, who coaches professional cyclists, brought the methodology from elite sport into mainstream culture. Zone 2 is now the most discussed training concept in health-forward circles.

For the Treasure Valley, this methodology fits the terrain. The Boise Greenbelt gives you miles of flat riverside running. The Foothills trails are perfect for hiking or riding at a steady aerobic pace. Idaho summers are long, and the geography rewards this kind of training. The question is not whether Zone 2 is right for you. It is whether you are actually getting into the zone, or just thinking you are.

The Dehydration-Heart Rate Problem

Here is the physiology that matters for Zone 2: when you are mildly dehydrated, your blood volume drops. Your heart has to pump faster to deliver the same amount of oxygen to working muscles. Research puts the number at a 5-10 BPM increase at exercise intensity for every 1-2% of body weight lost to dehydration. For a 175-pound person, 1% dehydration is less than two pounds of fluid. You can get there before you even feel thirsty.

In Zone 2, that heart rate bump is a real problem. If your Zone 2 ceiling is 145 BPM and dehydration has nudged you up to 148 or 150, you have crossed into Zone 3. Zone 3 is what coaches call "junk miles." You are working harder without getting the same mitochondrial stimulus, accumulating fatigue without accumulating the adaptation.

Boise hits 100-degree days routinely from late June through August. Sweat rates increase, fluid losses accelerate, and the dehydration window gets shorter. If you are heading out for a 60-minute Greenbelt run in July heat without being well-hydrated before you start, you may never fully enter Zone 2 at all.

Why Boise Tap Water Makes Staying Hydrated Harder

Boise and Meridian use chloramines for water disinfection. Chloramines are a combination of chlorine and ammonia, and municipalities use them because they last longer in the distribution system than free chlorine. That is useful for water safety. But it creates a taste and odor profile many residents describe as chemical, pool-like, or flat.

One of the most consistent findings in hydration behavior research is that people drink significantly more water when it tastes better. When tap water carries a chemical aftertaste, people substitute: a flavored drink, a sports drink with sugar, a bottled water, or nothing at all. None of those outcomes serve Zone 2 training.

With Boise's 2026 Drought Emergency Ordinance now in effect, outdoor water use is restricted and the municipal system is under increased demand during summer heat waves. During high-demand periods, water can run warmer through distribution lines, which amplifies the odor of disinfection byproducts. The ordinance does not change what is in your pipes, but the conditions it reflects, drought, heat, high usage, tend to make tap water taste worse at exactly the time you are training hardest.

The Electrolyte Angle (The Detail Zone 2 Athletes Miss)

Zone 2 training has spawned a cottage industry in electrolyte supplementation. LMNT, Nuun, Liquid IV, and similar products are designed to restore sodium, potassium, and magnesium lost through sweat. For longer Zone 2 sessions they can genuinely help.

Here is what most Boise athletes do not consider: Treasure Valley water hardness runs 12-17 grains per gallon, primarily calcium and magnesium dissolved in the water. When you mix an electrolyte packet into hard tap water, you are not starting from a neutral mineral baseline. You are adding sodium and potassium to water that already has elevated calcium and magnesium, which distorts the ratio the packet was formulated to deliver. Soft, filtered water gives your supplement a clean baseline to work from.

You can read about how hard water affects your recovery stack for more on the mineral interaction side of this.

What Soft, Filtered Water Does for Your Training

A water softener removes dissolved calcium and magnesium. A quality filtration system, often paired with a softener, addresses chloramines and taste-affecting compounds. The practical result for a Zone 2 athlete is straightforward.

• You drink more water. When tap water tastes neutral and clean, it becomes the default. Most people who install a softener and filtration system report hitting their daily water targets without tracking them.
• Your electrolyte supplements work as designed. A clean mineral baseline means the sodium, potassium, and magnesium ratios in your packet perform the way the formulator intended.
• Summer hydration becomes passive. With Boise's drought restrictions limiting outdoor use, your indoor water quality is your primary tool for managing heat and training load.
• Recovery equipment lasts longer. Many Zone 2 athletes use humidifiers for bedroom recovery. Hard water creates limescale buildup. Soft water eliminates the problem.

When water tastes good, you drink it consistently. Consistent hydration before, during, and after Zone 2 sessions is what keeps your heart rate in range and your adaptations accumulating. It is friction reduction, not a complicated protocol.

See how water quality interacts with broader athletic performance in our piece on why elite athletes pay attention to their water.

The Simplest Zone 2 Upgrade You Have Not Thought About

A solid Zone 2 setup adds up fast. A quality heart rate monitor, running shoes, a chest strap for accuracy, a Garmin or Whoop device. You are easily at several hundred dollars before you have logged a single session.

The water question is different because you are already paying for water. You are not adding a new line item; you are upgrading what comes out of your tap. The softener and filtration system has a one-time installation cost and then pays its way across plumbing protection, appliance life, soap savings, and training quality.

If you have never tested your water, you do not know your actual hardness number. The Treasure Valley range of 12-17 GPG is an average; your specific address may differ.

Frequently Asked Questions